Abstract
This BIP proposes additional query keys to the URI scheme for making Bitcoin payments that are automatically converted to a different currency by address owner.
Motivation
The purpose of these additional query keys is to enable users to easily view destination currency and exchange rate at which their Bitcoin payment will be converted to by address owner. The rates are also time-bound by an expiration timestamp.
Bitcoin does not know its exchange rate against USD/JPY/CNY/XAU. Any currency conversion scheme at protocol level is pretty meaningless.
Yes, of course but the person/entity who generates the URI does. Or more accurately, they would be the one to set the rate.
This proposal doesn't care about how valid or accurate an exchange rate is. It's only meant to standardize the way in which users are presented with what a bitcoin transaction is meant for.